Melatonin & Serotonin Syndrome

Melatonin and serotonin are two naturally occurring substances found in your body. Your pineal gland produces melatonin, and your intestinal cells and brain’s nervous center produces serotonin. Both melatonin and serotonin play several roles in human behavior and cognition. Serotonin syndrome is a medical condition defined as excess levels of serotonin in your body.

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Melatonin is the predominant hormone secreted by the pineal gland. Your body synthesizes melatonin from the amino acid tryptophan found in foods such as dairy, dried dates, chocolate and oats. Melatonin plays a key role in regulating your circadian rhythms including the awake-sleep cycle. Enzymes secreted by your hypothalamus control the synthesis and secretion of melatonin. Your body activates these enzymes as a result of darkness and depressed environmental light.


Serotonin is a neurotransmitter found in your gastrointestinal tract, platelets and central nervous system. Tryptophan is a building block of serotonin as well as of melatonin. Tryptophan is an essential amino acid, meaning that you cannot synthesize it in your body, but must obtain it from dietary sources. In your central nervous system, serotonin helps to regulate mood, sleep and appetite. Serotonin also has some effects on cognitive functions including memory and learning. Several antidepressants act mainly by modulating serotonin.

Serotonin Syndrome

Once your body uses serotonin, the neurotransmitter can either go back into storage vesicles or metabolize by the enzyme monoamine oxidase, or MAO. Certain drugs block the action of MAO and cause an accumulation of serotonin in your body. Serotonin accumulation in your body can result in serotonin syndrome. Characteristics of serotonin syndrome include variable alterations in cognition and behavior, autonomic nervous system function and neuromuscular activity. Symptoms of serotonin syndrome include altered mental status, spontaneous trembling of your group muscles, an excessive response of reflexes and excessive sweating.

Melatonin and Serotonin

Melatonin can synthesize from serotonin. However, an association between serotonin syndrome and melatonin has not been established through clinical research. Nonetheless, serotonin plays a function in the process of sleep and wakefulness. The gastrointestinal tract is the second major source of your body's melatonin. Enterochromaffin cells produce melatonin and release it into your blood after ingestion a meal. This melatonin released after a meal may contribute to feeling tired after a meal. However, clinical research has not confirmed that melatonin directly causes this feeling of tiredness after eating.